The present invention relates to radio frequency or microwave receivers, and more particularly to a method of improved video bandwidth resolution in Discrete Fourier Transform (DFT) based spectrum analysis.
In traditional swept spectrum analyzers, video bandwidth (VBW) filtering is used to reduce noise effects for displayed signal amplitudes. For example, a video filter is typically implemented as a low-pass filter placed after a log envelope detector and can be used to detect signals close to a certain noise level.
DFT based spectrum analyzers have emerged as a compelling measurement tool in relation to swept spectrum analyzers due to their capability of vector analysis, the combination of fast measurement times with wide spans and low resolution bandwidth (RBW), and real-time capabilities such as Digital Phosphor Spectrum Analysis (DPSA). However, architecture differences have not allowed traditional VBW filtering methods to be used on DFT-based spectrum analyzers.
Although DFT-based spectrum analyzers can emulate the effect of video filtering using trace averaging, trace averaging uses a discrete number of spectrum traces and therefore results in a coarse resolution in the available VBW values. Further, many standards such as the Worldwide interoperability for Microwave access (WiMax), the Global System for Mobile communications (GSM), and also government emission tests specify requirements based on a specific VBW. What is desired is a method of improved video bandwidth resolution in DFT-based spectrum analysis.